Characterization and applications of evoked responses during epidural electrical stimulation

Nishant Verma, Ben Romanauski, Danny Lam , Luis Lujan, Stephan Blanz, Kip Ludwig, Scott Lempka, Andrew Shofstall, Bruce Knudson, Yuichiro Nishiyama, Jian Hao, Hyun‑Joo Park, Erika Ross, Igor Lavrov. and Mingming Zhang

Abstract

Background
Epidural electrical stimulation (EES) of the spinal cord has been FDA approved and used therapeutically for decades. However, there is still not a clear understanding of the local neural substrates and consequently the mechanism of action responsible for the therapeutic effects.

Method
Epidural spinal recordings (ESR) are collected from the electrodes placed in the epidural space. ESR contains multi-modality signal components such as the evoked neural response (due to tonic or BurstDR™ waveforms), evoked muscle response, stimulation artifact, and cardiac response. The tonic stimulation evoked compound action potential (ECAP) is one of the components in ESR and has been proposed recently to measure the accumulative local potentials from large populations of neuronal fbers during EES.

Result
Here, we first review and investigate the referencing strategies, as they apply to ECAP component in ESR in the domestic swine animal model. We then examine how ECAP component can be used to sense lead migration, an adverse outcome following lead placement that can reduce therapeutic efcacy. Lastly, we show and isolate con‑ current activation of local back and leg muscles during EES, demonstrating that the ESR obtained from the recording contacts contain both ECAP and EMG components.

Conclusion
These findings may further guide the implementation of recording and reference contacts in an implant‑ able EES system and provide preliminary evidence for the utility of ECAP component in ESR to detect lead migration. We expect these results to facilitate future development of EES methodology and implementation of use of diferent components in ESR to improve EES therapy.